D. J. McLeod

New redshift z ≃ 9 galaxies in the Hubble Frontier Fields: implications for early evolution of the UV luminosity density

We present the results of a new search for galaxies at redshift z ≃ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with H_160 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H_160 and J_140. The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin2, which yields 12 galaxies at 8.4 8.4 sources reported by Zheng et al. In the MACSJ0416.1−240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z ≃ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ≃ 9 galaxies from the MACSJ0416.1−240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z ≃ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z ≃ 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization.

The z = 9-10 galaxy population in the Hubble Frontier Fields and CLASH surveys: the z = 9 luminosity function and further evidence for a smooth decline in ultraviolet luminosity density at z≥ 8

We present the results of a search for z=9-10 galaxies within the first 8 pointings of the Hubble Frontier Fields (HFF) (4 clusters plus 4 parallel fields) and 20 cluster fields from the CLASH survey. Combined with our previous analysis of the Hubble Ultra-Deep field (HUDF), we have now completed a search for z=9-10 galaxies over ~130 sq. arcmin, across 29 HST WFC3/IR pointings. As in our recent study of the first two HFF fields, we confine our primary search for high-redshift candidates in the HFF imaging to the uniformly deep (i.e. sigma_160>30 AB mag in 0.5-arcsec diameter apertures), relatively low magnification regions. In the CLASH fields our search was confined to uniformly deep regions where sigma_160>28.8 AB mag. Our SED fitting analysis unveils a sample of 33 galaxy candidates at z_phot>=8.4, five of which have primary photometric redshift solutions in the range 9.6 =8. We conclude that the data continue to support a smooth decline in rho_UV over the redshift interval 6<z<10, in agreement with simple models of early galaxy evolution driven by the growth in the underlying dark matter halo mass function.

The evolution of the equivalent width of the Hα emission line and specific star formation rate in star-forming galaxies at 1 < z < 5

We present the results of a study which uses spectral energy distribution (SED) fitting to investigate the evolution of the equivalent width (EW) of the Halpha emission line in star-forming galaxies over the redshift interval 1 =1 in the CANDELS UDS and GOODS-S fields. Confining our analysis to a constant stellar mass range (9.5<log(M/Msun)<10.5), we find that the median EW(Ha) evolves only modestly with redshift, reaching a rest-frame value of EW(Ha)=301+/-30 Angs by redshift z~4.5. Furthermore, using estimates of star-formation rate (SFR) based on both UV luminosity and Ha line flux, we use our galaxy samples to compare the evolution of EW(Ha) and specific star-formation rate (sSFR). Our results indicate that over the redshift range 1<z<5, the evolution displayed by EW(Ha) and sSFR is consistent, and can be adequately parameterized as: propto (1+z)^(1.0+/-0.2). As a consequence, over this redshift range we find that the sSFR and rest-frame EW(Ha) of star-forming galaxies with stellar masses M~10^(10) Msun are related by: EW(Ha)/Ang=(63+/-7)sSFR/Gyr^(-1). Given the current uncertainties in measuring the SFRs of high-redshift galaxies, we conclude that EW(Ha) provides a useful independent tracer of sSFR for star-forming galaxies out to redshifts of z=5.

Unveiling the nature of bright z ~ 7 galaxies with the Hubble Space Telescope

We present new Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) imaging of 25 extremely luminous (−23.2 ≤ MUV ≲ −21.2) Lyman-break galaxies (LBGs) at z ≃ 7. The sample was initially selected from 1.65 deg2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman α emitters, ‘Himiko’ and ‘CR7’. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW0(Hβ + [O III]) > 600 A). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z ≃ 7 galaxies, and ubiquitous at the very bright end (MUV 1000 similarly bright galaxies at z ≃ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.

ACCOUNTING FOR COSMIC VARIANCE IN STUDIES OF GRAVITATIONALLY-LENSED HIGH-REDSHIFT GALAXIES IN THE HUBBLE FRONTIER FIELD CLUSTERS

Strong gravitational lensing provides a powerful means for studying faint galaxies in the distant universe. By magnifying the apparent brightness of background sources, massive clusters enable the detection of galaxies fainter than the usual sensitivity limit for blank fields. However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this {\it Letter}, we demonstrate there is an associated increase in the cosmic variance uncertainty. As an example, we show that the cosmic variance uncertainty of the high redshift population viewed through the Hubble Space Telescope Frontier Field cluster Abell 2744 increases from ~35% at redshift z~7 to >~65% at z~10. Previous studies of high redshift galaxies identified in the Frontier Fields have underestimated the cosmic variance uncertainty that will affect the ultimate constraints on both the faint end slope of the high-redshift luminosity function and the cosmic star formation rate density, key goals of the Frontier Field program.

Characterizing the evolving K-band luminosity function using the UltraVISTA, CANDELS and HUDF surveys

We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z ≤ 3.75, based on a nested combination of the UltraVISTA, Cosmic Assembly Near-infrared Deep Legacy Extragalactic Survey and HUDF surveys. The large dynamic range in luminosity spanned by this new data set (3–4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z ≥ 0.25 is relatively steep (−1.3 ≤ α ≤ −1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new data set, we find that a double Schechter function provides a significantly improved description of the KLF at z ≤ 2. At redshifts z ≥ 0.25, the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (MK ≥ −20.5) or bright magnitudes (MK ≤ −24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at MK ≃−23 dropping by a factor of ≃5 over the redshift interval 0.25 ≤ z ≤ 3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (α1 = −0.5, α2 = −1.5) and a shared characteristic magnitude (M⋆K MK⋆). According to this parametrization, the normalization of the component which dominates the faint end of the KLF remains approximately constant, with ϕ⋆2 ϕ2⋆ decreasing by only a factor of ≃2 between z ≃0 and 3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z ≃3. Finally, we note that within this parametrization, the observed evolution of M⋆K MK⋆between z ≃0 and 3.25 is entirely consistent with M⋆K MK⋆ corresponding to a constant stellar mass of M⋆ ≃5 × 1010  M⊙ at all redshifts.

The VANDELS ESO public spectroscopic survey

VANDELS is a uniquely deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO’s Very Large Telescope (VLT). The survey has obtained ultradeep optical (0.48 < λ < 1.0 μ m) spectroscopy of ≃2100 galaxies within the redshift interval 1.0 ≤ z ≤ 7.0, over a total area of ≃0.2 deg2 centred on the CANDELS Ultra Deep Survey and Chandra Deep Field South fields. Based on accurate photometric redshift pre-selection, 85 per cent of the galaxies targeted by VANDELS were selected to be at z ≥ 3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high-signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities, and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < tint< 80 h), the VANDELS survey targeted: (a) bright star-forming galaxies at 2.4 ≤ z ≤ 5.5, (b) massive quiescent galaxies at 1.0 ≤ z ≤ 2.5, (c) fainter star-forming galaxies at 3.0 ≤ z ≤ 7.0, and (d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multiwavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper, we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design, and target selection.

The relationship between dust and [C i] at z = 1 and beyond

© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

The VANDELS ESO public spectroscopic survey: observations and first data release

RJM, AM, EMQ, and DJM acknowledge funding from the European Research Council via the award Consolidator Grant (P.I. R. McLure) AC acknowledges grant PRIN-MIUR 2015 and ASI n.I/023/12/0. PC acknowledges support from CONICYT through the project FONDECYT regular 1150216. RA acknowledges support by ERC Advanced Grant 695671 “QUENCH”. FB acknowledges support by Fundacao para a Ciencia e a Tecnologia (FCT) via the postdoctoral fellowship SFRH/BPD/103958/2014 and through research grant UID/FIS/04434/2013.